1. BackgroundSo far about one hundred PM vacuum system deskstop studies have been carried out. Conclusion has been, that more than 50 % of the systems suffer of poor efficiency.
Is has been diffucult to specify, what are the machines that need improvement, and which do not. This article gives simple quidelines for the bencmarking.
2. Benchmarking of PM vacuum system energy consumptionPM vacuum system Speficic Energy Consumption ( SEC, kWh/tn) is one simple way to estimate the state of the existing system.
At the following is presented some typical energy consumption levels for different paper grades ( see pictures 1 and 2 ). This data is collected from the vacuum system studies during 2007 - 2011.
More detail data is available today, but for benchmarking purposes attached pictures give a good starting point.
Picture 1: PM vacuum system SEC as a function of PM speed.
Picture 2: PM vacuum system SEC as a function of basis weight.
3. Variation between the machinesThere exists large variation based on paper grade and machine consept, which makes it difficult give exact conclusions. However, if SEC of PM vacuum system is lower than average, most probably savaing potential is small. For example 40 kWh/tn is good level for heavy board grades, but for low grammage fine papers 70 kWh/tn can be acceptable.
Also in case the electric energy consumption is over 80 kWh/tn, most probably improvement potential always exists.
Vary many machines fall in the middle area, and in these cases the only way to find out the energy saving potential is to make a more detail study.
In many cases it is possible to improve the efficiency ( = decrease energy consumption) with relatively simple improvements without installation of expensive new equipment. If the pay-out time of 4 years could be accepted, improvement potential can be found from most of the machines.
4. Desktop studyEnergy analysis should always be started by doing a desktop study. In order to do it, normally the PI diagram and DCS prints ot the vacuum system operation conditions already give a good starting point.
Further actions can be decided based on this desktop study. If energy saving potential exists, a more detail engineering including field measurements is needed to specify the required actions and pay-out time of the required investments.
5. SummaryPlease, do the benchmarking first. It is atways the first step.
- When it has been done, further actions can be started.